A variety of processes for making products, including products in the food and pharmaceutical industries, utilize steps with particles in suspension for use in a variety of applications. In one example, it has been proposed to deliver certain types of drugs to patients by inhalation of powder particles as a delivery mechanism. One particular example uses microparticles comprising diketopiperazine, known as Technosphere® microparticles. The Technosphere microparticles have a platelet surface structure and can be loaded with a drug. One use of these microparticles is for the delivery of insulin by inhalation.
An exemplary process for making Technosphere microparticles begins with raw materials, including acetic acid and fumaryl diketopiperazine (FDKP) to precipitate the Technosphere particles out of solution to form a suspension. Using a tangential flow filter, the particles are washed using diafiltration, and the concentration of the particles is increased by removing liquid. Insulin is added to the suspension to form a Technosphere Insulin (TI) suspension. The suspension is flash frozen to make pellets that are dried in a bulk lyophilization process to remove the liquid components. Dry TI powder removed from the lyophilizer is packed into containers for later filling of inhaler cartridges.
During manufacturing of Technosphere Insulin, a process tank receives the suspension of Technosphere particles after the tangential flow filtration and concentration steps at approximately 10% solids by weight. The suspension is stirred continuously prior to and during insulin addition. Insulin solution preparation does not proceed until an actual percent solids value of the suspension is determined.
Existing methods for determining percent solids of Technosphere particles in the suspension are slow and are subject to errors. One existing method involves taking one or more samples of the Technosphere suspension, drying the suspension in a microwave oven and weighing the remaining solids. The process typically requires two to three hours and is subject to measurement errors.
Accordingly, there is a need for improved methods and apparatus for determining percent of solids in a suspension.